While I am at, it was France and Great Britain's behavior at the End of World War One that lead to World War Two.
When the USA had a greater hand in it, We ( THE USA ) instituted the Marshal Plan. Which saved Post War Germany. We had trials For your great wise worldly and culturally advanced leaders, Not mass executions like Some allies wanted. We didn't have the Massive " Rape fest " that the Soviets promoted in Berlin. And it was the USA that fed Germany and got it on its feet and protected it from the USSR.
When the biggest impact your country has had on modern history is " The Death Camp " I would think you would be more tolerant when a nation at least tries to do it correctly.
First off you can't blaim the UK or France for causing WWII, well you can just not solely. There were hundreds of contributing factors, a few of which can be blaimed upon the USA.
First the Wall Street crash, caused the US to call in billions of dollors (or marks) in loans, this led to the second depression in Germany, which is understood to be one of the factors that allowed Adolf Hitler and the Nazi party (after failing once) to come to power. If the US had allowed Germany a decent ammount of time to pay back these loans then it is pluasable that there could have been no war, obvioulsy it is unlikely considering the instability of the Weimar Republic but it was a factor.
Second for most of WWII America stood watching, it was only once they were directly attacked that the US got into the war, D-Day had already been planned and formulated but was then backed up by US troops, now I am not saying and never would say that all the US troops that died on the beaches of normandy died in vain, but the Allies would most likely of began pushing back the Nazi troops, the US marines allowed the attack to be much more effective and in practice end the war, the fact still remains that without the US the war (in europe) would still have been won.
The war in the pacific is a topic I do not know much about, but I can say that the US here did have a complete victory, with little or no aid from anyone else.
Now post WWII the Allies did not want to simply line up and shoot every single Nazi, yes a few high rankers of the Allies wanted a few influencial Nazi members killed, but their crimes envolved killing of innocent people, for no other reason then the relgion they belong to, the colour of their skin or the culture they were born into.
Now,on topic, I beleive that at this moment, no-one who has access to nuclear armaments would fire them on any other country, for the simple fact that the reaction from every other nuclear power would be to fire apon them. However as soon as 100% effective missle defene systems begin to become reality this may change.